1. Field of the Invention
The present invention relates to an electronic device system in which a plurality of electronic devices are connected to a network via an IEEE 1394 bus, and relates to a technique for reducing bus bandwidth usage when powering on and off a connected electronic device by remote control via the bus from another device.
2. Description of the Related Art
In recent years, IEEE 1394 serial bus (IEEE Std 1394-1995 Standard for a High Performance Serial Bus, which is hereinafter referred to as “IEEE 1394”) interfaces have become widespread as digital data interfaces to network digital electronic devices including audio-video devices such as a set-top box (hereinafter referred to as “STB”), a digital television, a digital video cassette recorder (DVCR), and a DVD recorder. This IEEE 1394 is a serial bus that can be used by a plurality of digital electronic devices on a network to exchange digital data between each other or to control each other.
In such a system where a plurality of electronic devices are connected via an IEEE 1394, one of the electronic devices (referred to as “device P”) controls the power supply of another device (referred to as “device Q”) on the same IEEE 1394 in the following manner. For example, when the device P powers on the device Q, the device P sends to the device Q an AV/C power control command of AV/C Digital Interface Command Set (hereinafter referred to as “AV/C commands”) with power_state=POWER ON. After the sending, the device P typically continues to periodically send an AV/C power status command to inquire the power status of the device Q until the device Q changes to the power-on state. Thereby, the device P checks whether or not the power status of the device Q has changed. However, this periodical sending of the command increases the amount of bandwidth used on the IEEE 1394 bus, thus reducing the efficiency in the use of the bus.